Keshav Kant

Bio: Keshav Kant is an academic researcher. The author has contributed to research in topics: Capillary action & Adiabatic process. The author has an hindex of 1, co-authored 3 publications receiving 6 citations.

A model for helical capillary tubes for refrigeration systems

Abstract: This paper presents a flow model that has been developed to design and study the performance of helical capillary tubes and to mathematically simulate a situation closer to that prevailing in practice. Homogeneous flow of twophase fluid is assumed through the adiabatic capillary tube. The model includes the second law restrictions. The effect variation of different parameters like condenser and evaporator pressures, refrigerant flow rate, degree of subcooling, tube diameter, internal roughness of the tube, pitch and the diameter of the helix on the length of the capillary tube are included in the model. Theoretically predicted lengths of helical capillary tube for R-134a are compared with the length of the capillary tube needed under similar experimental conditions and majority of predictions are found to be within 10% of the experimental value.

An equilibrium model and assessment of the effect of metastability for straight adiabatic capillary tubes

Abstract: A numerical two-phase flow model is developed here for adiabatic capillary tubes in small capacity vapour compression refrigeration systems using alternative refrigerant (R-134a). The model is based on the fundamental equations of conservation of mass, energy and momentum that are solved simultaneously for a homogeneous flow under saturated, sub-cooled and two-phase conditions. The model also uses wellestablished empirical correlation for friction factor. The effect of sudden contraction at the capillary entrance is also considered in the model. To asses the effect of metastability; Chen’s model for the prediction of underpressure of vaporization is used. Using this value of under pressure of vaporization the change in the length of capillary and change in mass flow rate is determined to finally asses the percentage change in these parameter due to metastability.

Research Article A COMPARISON OF HOMOGENEOUS AND DRIFT FLUX MODEL FOR CAPILLARY TUBE

Abstract: Theoretical work on capillary tube started with homogeneous flow models assuming the effect of slip between the two phases to be negligible as the diameter of such capillary tubes is very small. In the recent years the work on separated flow model considering the slip between the liquid and vapour phases have started picking up. In the present paper an attempt is made to consider the slip between the phases and apply ‘drift flux model’ to simulate the flow of refrigerant through adiabatic capillary tube and compare it with the homogeneous model. The models use well established empirical correlations for friction factor for single phase flow and two phase flow. Comparison of the models with the experimental values available in the literature is made.

Dynamic model and experimental study of an air–water heat pump for residential use

Abstract: This paper presents a study of the dynamic behavior of a vapor compression heat pump for residential water heating. The mathematical models for heat exchangers are formulated by using mass, momentum, and energy conservation equations, while capillary tube model is based on the equations of conservation of momentum. The model is formulated from the manufacturer experimental data and the energy conservation balance. The contribution of this study to the field of dynamic modeling appears on the convergence of models of heat exchangers, this being accomplished with a variable error in spatial and time minimizing the instabilities in the calculation. The coupling among the four components allows the determination of the spatial and temporal profiles of temperatures, pressures and mass flow rates, as well as the refrigerant distribution in the heat exchangers during the water heating process. The validation of the model is done by comparison with the experimental results.

A generalized continuous empirical correlation for the refrigerant mass flow rate through adiabatic straight and helically coiled capillary tubes

Abstract: In spite of the simple geometry of capillary tubes, the refrigerant flow behavior through capillary tubes is complex. Numerous empirical correlations have been developed to predict the refrigerant mass flow rate through adiabatic helically coiled capillary tubes, but all of them have discontinuity problems at the saturated liquid line. In the present study, a generalized continuous empirical correlation is developed that can be used to predict the refrigerant mass flow rate through adiabatic helically coiled capillary tubes as well as straight capillary tubes. The new correlation can accommodate both subcooled liquids and saturated two-phase flow conditions in the capillary tube inlet condition. The proposed new correlation is validated with experimental data for R-22, R-134a, R-407C, R-410A, and LPG. In addition, the new correlation was compared with previous empirical correlations available in the open literature. The present correlation showed excellent performance in terms of its application range and degrees of continuity and accuracy.

An experimental study of the Effect of capillary tube diameter and configuration on the performance of a simple vapour compression refrigeration system

Abstract: The study of the expansion device in the simple vapour compression refrigeration system is necessary in order to understand the parameters which can enhance the overall performance of the system. The experimental study was done on the capillary tubes of 31 gauge, 36 gauge and 40 gauge and each test section was studied with three distinct configurations i.e. helical coiled, straight coiled and serpentine coiled configuration. The effect of the configuration and the capillary tube diameter on the overall performance of the system was studied. The findings of the experimental study revealed that the mass flow rate is maximum for the straight configuration and is least for the helical coiled configuration. The refrigeration effect was found to be maximum for the helical coiled configuration and was found to be least for straight coiled configuration. The compressor work was found to reduce as the load was increased on the system. Decreasing the capillary tube diameter increased the mass flow rate in the system and decreased the refrigeration effect produced.

Assessment of Dimensionless Correlations for Prediction of Refrigerant Mass Flow Rate Through Capillary Tubes — A Review

Abstract: Capillary tubes are widely used as expansion devices in small-capacity refrigeration systems. Since the refrigerant flow through the capillary tubes is complex, many researchers presented empirical dimensionless correlations to predict the refrigerant mass flow rate. A comprehensive review of the dimensionless correlations for the prediction of refrigerants mass flow rate through straight and coiled capillary tubes depending on their geometry and adiabatic or diabatic capillary tubes depending on the flow configurations has been discussed. A comprehensive review shows that most of previous dimensionless correlations have problems such as discontinuity at the saturated lines or ability to predict the refrigerant mass flow rate only for the capillary tube subcooled inlet condition. The correlations suggested by Rasti et al. and Rasti and Jeong appeared to be general and continuous and these correlations can be used to predict the refrigerant mass flow rate through all the types of capillary tubes with wide ...

Effect of capillary tube on the performance of a simple vapour compression refrigeration system

Abstract: It is essential to study the effect of capillary tube geometry on the performance of refrigeration systems. The literature review focuses on the effect that geometrical parameters like capillary tube length, bore diameter, coil pitch, number of twist and twisted angle have on the pressure drop, coefficient of performance (COP) and mass flow rate of the system. These parameters can be further studied using physical models and mathematical modeling concepts. The parameters stated above can be further optimized in order to enhance the performance of the refrigeration system.